The present invention pertains to a one-piece, refractory ceramic composite body consisting of at least two layers located next to one another as well as to a process for manufacturing same.
Such a composite body has been known from DE 41 08 153 A1. It is called a "refractory molding" there and it has at least two nonmetallic shells that envelope one another at least partially.
Moldings and composite bodies of this type are used, e.g., as wearing parts in the spouts of metallurgical vessels (so-called nozzles, pouring spouts and channels, submerged pipes, but also as sliding plates or the like).
The prior-art refractory molding comprises essentially an inner shell and an outer shell, which are prefabricated in a tubular shape. While the outer shell is said to consist essentially of carbon-bound aluminum oxide according to one embodiment, zirconium dioxide is selected as the material for the inner shell.
The material for the outer shell was selected from the viewpoint that the outer shell shall be able to be heated inductively in an electromagnetic field. It is achieved as a result that the inner shell can be preheated slowly and uniformly to a value close to its operating temperature. The risk of cracking is avoided as a result. Due to the inductive heating of the inner shell, it assumes the conduction of heat to the outer shell.
To prepare the prior-art refractory molding, it is necessary to prefabricate the inner shell and the outer shell separately and to subsequently prepare a composite body. This is difficult, among other things, even because of the small wall thicknesses of the moldings.
A refractory casting sleeve for a metallurgical vessel, which consists of, e.g., zirconium carbide and has an inner carbon coating, has been known from FR-PS 1 525 154. The casting sleeve is surrounded by an induction coil, by means of which the casting sleeve is heated.
According to the suggestion made in EP 0 379 647 B1, the induction coil is part of the inner wall of a multilayer, refractory ceramic tubular body.
A process for the inductive heating of a molding made of ceramic material, which does not couple inductively at room temperature, but can be coupled to the field of the inductor at increased temperature, is described in DE 43 01 330 A1. The tubular molding consists of zirconium dioxide, which is practically electrically nonconductive at ambient temperature but which develops electric conductivity at increased temperatures, beginning at, e.g., 800.degree. C. The molding is provided on the inside with a coating that is electrically conductive even at room temperature.
The refractory nozzle according to DE 44 28 297 A1 consists of a wear-resistant core consisting of zirconium dioxide, which is provided with a pouring opening, and a jacket surrounding same, consisting of a carbon-bound ceramic material, which can be heated inductively beginning from room temperature. The jacket is shaped around the prefabricated core and is compacted.
The inductive heating of the said refractory ceramic wearing parts represents a considerable technological progress over conventional methods of preheating (e.g., by direct exposure to burner flames), because a uniform, "soft" heating of the component is achieved, so that chipping off or cracking due to different heat zones in the component can be practically ruled out. As a result, the essential safety of such parts is substantially increased, for example in the spout area of a metallurgical melting vessel.